LS1 PCM mounting under dash
 

Just a quick question.. with the new hawks headers i dont feel to safe running the pcm where i had it on frame channel there and am going to put it in the car by running the wiring thru the wirewall just under the heater box... there is a tiny hole there i will just punch it out to whats needed

What is the smallest sized hole I need to punch in there.. i just dont wanna try and do it twice like the damn clutch :)

Ive seen it somewhere in this forum but cant find it :(

Pics would be kew too :)

here is a pic of Mr. Dude's way

yep thats what im lookin for.. hopin he pipes in :)

IF i remember correctly he used a 2" hole saw to do it. Thats what im going to do pretty soon. Take some pictures of it and post it bro

Did/Are you guys modifying the stock harness to reach in there or is it long enough already?

According to Mr. Dude, the LS1 harness is just long enough to make it to the stock location. I havent tried it yet but my time is coming really quick LOL

eww thats a nasty pic. heh.


the hole size is dictated by the largest connector that has to go thru it.. from how i measured, the way to do it with the smallest hole is to feed the PCM connectors back thru it.. so you need the hole JUST big enough to fit them thru.

pop the protective top cover off of the PCM connectors, and you can just squeeze them in... i honestly forgot the size now... its been over a year.

just be sure to drill your hole BELOW the HVAC box on the inside of the car and above the level of the "framerail".

the PCM does not fit vertically like the stock one did, however, theres still plenty of room for it under there.

I wish there was a better pic :) So do i need to take off my HVAC unit in the engine bay in order to drill the hole?

its a good ideal to take it out anyway, its a tight fit putting the ls1 in and to prevent damage to the box its just a good idea to take it out. plus its easier to "thread" the wires thru the hole you just drilled.

id take it off just to do the engine swap.. that thing is huge. :lol:
plus leaving it in gives you a good chance to smash the engine into it and breaking it, or your coil pack.

i dont have pics offhand, but i found some old pics on my work computer.
the translucent circle is where the hole goes. you can see the dusty remains of where the box was... leave the dust there as a ref marking until you're ready to re-assemble.. its useful.

note:
it is below the HVAC box, both inside and outside the car.
it is NOT flush with the framerail.... dont make it flush unless you want water in your car.. just because you have a grommet wont make it perfectly weather tight.

lol, you jumped in while i was photoshopping thoes circles in.. :lol:

Those are much better pics Mr. DUDE :) I guess i have to take it off then. It will be worth doing just to make the engine bay look alot cleaner.

It definitely does. Just got done relocating the PCM to the passenger side in the car. Here are some pics.


We ended up moving the battery over to the drivers side and moved the fuse box to the passenger side. This way we only needed to extend maybe 8-10 wires at most.
https://www.ls2.com/boggs/83wire/P1003257.jpg


We put the hole where it was suggest in this thread. Worked out good, but we accidentally cought the frame rail and had to repair a small hole on the bottom side to make sure no water would get in.
https://www.ls2.com/boggs/83wire/P1003258.jpg

This is the inside view. We had so much wire left over for some connections we brought it into the cabin as well and hid it behind the carpet.
https://www.ls2.com/boggs/83wire/P1003259.jpg

The heater box sucked. I hopfully will never have to take that thing out againg. Uhg. Carnage of the dash..
https://www.ls2.com/boggs/83wire/P1003260.jpg


I don't have a pic, but we picked up a small peice of aluminum and jb-welded it to protect the harness from the exhaust manifold. we had pretty good cleareance any way, but since we were down there we though it would be a good idea. ;)

After trying to get the heater box on and failed, i really thinking of putting the PCM into the engine bay??? I dont want to, but all my wire connections will be right under there. Im not sure if i should keep trying or what :( Looks like you might have to take the passenger side coils off just to fit the air box, how did you do it dingle??

joey

Yea we took the coils off to make it easier. The PCM looked nasty in the engine bay that's why I moved it. The hardest part for us was the top right bolt looking head on at the car of the heater box. It was almost impossible to get to from the inside after unbolting pretty much everything on the dash. Ended up using a pair of vice grips to hold the bolt while we unscrewed the nut in the engine bay. You can see the vice grips in this pic. https://www.ls2.com/boggs/83wire/P1003258.jpg

Getting it back on was a piece of cake for us. :shrug:

I dont think i have that problem that you have, using the vise grips.... Well in that case i think i will give it another shot. The car runs really good, so i know that the wire is fine. Thanks bro

so what exactly is your problem with the heaterbox?


if its not fitting, its probly hitting on the coil/coilbracket/valvecover you need to trim the "flange edge" back a bit with the AC box...

one of the main reason is because of the coil and all the wire. But yesterday i got the PCM in the dash and put everyting back on in the car. LOOK REALLY GOOD:) im not going to takel the heater box till i go to the ref. and also put my tranny back on. But yeah looks like im going to trim some stuff.

Joey

I put mine just in front of the hgeater box like how it is in a fourth gen. Have yet to finish all of my wiring, but could get you guys some pics if wanted. It did require some grinding on the fins btw. Wouldve likd to put it in my dash, but didnt seem like it would make it.

i did mine just like mr.dude, works great.

Justin

so did I... Still kinda scared to put the heater box on :( going to be a VERY tight fit. But putting the PCM in the dash makes the engine bay WAY CLEANER!!!

Re: LS1 PCM mounting under dash
 

What did you guys do for grommets? I can't seem to find one even close to 2 inches.

Re: LS1 PCM mounting under dash
 

you can find several rubber plugs that size....

get a rubber plug.. drill/cut a hole in the center.. slit it so you can fit it over the wires.

done correctly, when you pop it in, it seals up nice and looks good... if you messed it up a bit.. a little black RTV will fix it... (if you messed it up alot, buy another plug.. its cheap. lol)

Re: LS1 PCM mounting under dash
 

I know that this is an old thread.. but could anyone out there take a picture of how your pcm is mounted? i can't seem to find a way for it to fit and still be able to put the lower kick panel back on properly

Re: LS1 PCM mounting under dash
 

I mounted mine horizontally with some big tie wraps and cinched it up to bellow the heater core area. My cover fits on fine but my car had no stock PCM there being a factory carb car so maybe thats a difference?

Re: LS1 PCM mounting under dash
 

There's a few threads around on how to mount it. Here are a couple pics of how I did mine. If you dont know what to look for, you'd never know it was there.

Attachment 427207

I used a piece of aluminum to hold the PCM in place. I used the two screws that held up the ECM bracket to hold the alum in place.

Attachment 427208

I cut a notch in the hush panel to fit around the harness, and it also sort of holds the back of the hush panel up in place.

Attachment 427209

And this is what everyone sees.

Attachment 427210

J.

Re: LS1 PCM mounting under dash
 

Another location you might want to concider is in the passenger front fender well, remove the plastic flashing above the tire and in the front corner of the fender well there is a spot that is a good fit. on the car normally it comes out that side and into the interior just reroute it to the front. There may be a few wires that need to be extended as well. If you check other gm cars the malabu has it in this location

Re: LS1 PCM mounting under dash
 

this is where I will be putting mine. Plenty of room and is the exact same place as the Corvete (C5).

Re: LS1 PCM mounting under dash
 

Meh. This works but it looks gacky on third gens as it dont really fit looking like it belongs there. Plus its really not any more difficult to mount it under the dash it may even be easier

Re: LS1 PCM mounting under dash
 

cam... I think 92tracker meant put it inside the fender. He mentioned removing the plastic liner, which to me meant he was mounting it inside. The vettes put it inside the fender I believe. I think what you are referring to is trying to mount it where the 4th gen f-bodies are mounted. Ive never been a fan of this...and on my car I couldnt even get it to work.

The inside the fender idea is actually pretty good. I think you could mount it without extending wires, as its closer to the engine bay than inside the car is. The PCM is weather proof...so its not like it'd get messedu p.

J.

Re: LS1 PCM mounting under dash
 

I just finish the mounting and put it in the fender and yes removing the plastic inner fender just like the corvettes. It was a good fit I will send out some pics later. Took it for a few test drives now comes the hard part getting the E-test. One other question the motor did not come with an air pump when I bought it. will it pass emisions without it or should I go out and put one on?

Re: LS1 PCM mounting under dash
 

this is what i did for mine, if you dont mind not having a/c or heat, depending on the climate you are in............... just run all the wiring through a/c blower hole into the inside. didnt have to cut or move anything fits perfect, cleans up engine bay a lot, reduces little bit of weight, and helps run wires!! again if you dont mind not having the heat or a/c.....

Attachment 184823

Re: LS1 PCM mounting under dash
 

i was planning on running mine inside the fender too. 92tracker u got any pics of that?

Re: LS1 PCM mounting under dash
 

I have the car put away for the winter and have not thought about sending pics I will send some out soon

Re: LS1 PCM mounting under dash
 

Rise up an old thread, but I ran mine through the stock location?

Re: LS1 PCM mounting under dash
 

So did I. Jon (pocket) extended my harness so that it would reach to the stock location on my car using the hole behind the passenger fender. I took a sheet of aluminum and bent a lip onto the end of it and screwed it in the spot where the factory ECM mount went, had the ls1 ECM secured to the aluminum so I ended up throwing away the old plastic holder.

Re: LS1 PCM mounting under dash
 

Good idea, like that. I was thinkin of maybe reusing the plastic unit, but not gunna happen.
I will have to get the ECM up in there to see where to fab that braket up.

Re: LS1 PCM mounting under dash
 

The LSx PCM is way too big to fit on the old plastic ECM tray

I wrapped mine with an old towel and slide it up in the same spot as the old ECM. Towel was to prevent vibrations. Fits awesome. Used a short length of romex solid core wire to hold the PCM up in there since it's such a tight fit and couldnt get any sort of bracket on it

Re: LS1 PCM mounting under dash
 

I used the plastic bracket, just had to cut it up a bit. Then I zip tied the computer to it to make sure it was secure, stuck it up in there, and replaced the screws. I may have had to drill new holes for the screws, I don't quite remember.

Re: LS1 PCM mounting under dash
 

oh how time, flies will try this weekend to pull the car out and get some pics

Re: LS1 PCM mounting under dash
 

Got any pics of this mounting?

Re: LS1 PCM mounting under dash
 

old post but can you please post those photos? I'm doing the swap now and would like to see how this looks.

Re: LS1 PCM mounting under dash
 

You can attach the LS1 ECM to the TPI bracket and put it in the stock location. I am doing it with my swap. I will try to remember to get a few pictures of what I did. I had to shave the one side down, cut the pin/nub down/off, and cut the big clip off the top and used some tie wraps to hold it to the bracket. it will fit up there like stock once you do it plus it will still have air space around it.

Re: LS1 PCM mounting under dash
 

If you mount the PCM in the stock location can you have the wires come through the firewall behind the engine so they're hidden more or is there not enough room there to do that?

Re: LS1 PCM mounting under dash
 

Here's where I ran mine:

Attachment 316299

With the HVAC housing back in, you can't see it.

I got this hole punch from Harbor Freight. I did side-by-side punches and trimmed them oval for the pass-through, lined the edges with door edge protector from NAPA, then ran the PCM connectors through.

Attachment 316300

Re: LS1 PCM mounting under dash
 

Same here basically, mostly to keep water from flowing in.
https://cimg7.ibsrv.net/gimg/www.thi...b88c5b2014.jpg
A dust boot for the jamb/door harness fits great, cut down afterward.
https://cimg1.ibsrv.net/gimg/www.thi...db0c0b259d.jpg
I used the stock ECM mount for the new ECM.
https://cimg5.ibsrv.net/gimg/www.thi...33abd70086.jpg